Throughout the world, wood is perhaps the most widely used fuel for cooking and heating and for heating is being used more and more in developed countries as an alternative to petroleum and natural gas. Wood is becoming more expensive, and, lately, considerable effort has been expended to increase the efficiency of wood-burning stoves so that they yield more heat per unit of wood burned and need to be recharged with less frequency. While burning wood, combustible volatiles are generated but only partially consumed. Some of the unburned volatiles escape up chimneys and contribute to air pollution while other volatiles condense as creosote on cool chimney surfaces and stove surfaces. The creosote can cause chimney fires or blockage and therefore must be periodically removed if one wishes to safely burn wood. In addition, a great deal of particulate matter becomes entrained in the stove exhaust contributing greatly to air pollution.
Modern wood-burning stoves are generally airtight with the exception of small controlled air inlets and are baffled in order to increase their efficiency. While the efficiency of these stoves is considerably enhanced, much of the combustible volatiles released by burning the wood is released into the atmosphere without being burned. In addition, these stoves produce almost as much smoke or particulate matter as fireplaces and stoves which are not airtight. The volatiles produced by airtight stoves also tend to condense on stove pipes and chimneys creating a fire hazard, and since they are not burned, the volatiles and particles do not contribute to the heat output of the stove.